Question 676824
x =  one number
y = another number
...
x+y=18
7y-2x = 36
...
Rearrange the first equation as x = 18-y
Substitute into the second equation
7y - 2(18-y) = 36
Distribute the 2
7y - 2(18) - 2(-y) = 36
7y - 36 + 2y = 36
Isolate the y variable
9y = 36 + 36 
9y = 72
Divide both sides by 9
{{{highlight_green(y=8)}}}
x = 18-8 = {{{highlight_green(x=10)}}}
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